Means for controlling self-exciting generators.



No. 829,133. PATENTED AUG. 21, 1906. B. P. W. ALBXANDERSON.

MEANS FOR CONTROLLING SELF EXCITING GENERATORS. APPLICATION FILED JULYZO. 1905.

Witnesses:

ww% Ernst F. WW/exanqerson.

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/n yen tor UNITED STATES PATENT OFFICE.

ERNsT F. w. ALEXANDERSON, or scHENEcTADY, NEw YORK, ASSIGNOR TO GENERAL ELEoTRic COMPANY, A CORPORATION OF NEW YORK.

MEANS FQR CONTIROLLING SELF-EXCITING GENERATORS.

Specification of Letters Patent.

Patented Aug. 21, 1906.

To all whom, it may concern."

Be it known that I, ERNST F. W, ALEXAN- DERsoN, a subject of the King of Sweden and Norway, residing at Schenectady, in the county of Schenectady and State of New adapted for use in connection with alternators of the type disclosed in Patent No. 789,476, issued to me May 9, 1905, but is not limited in all its aspects to this particular application.

Self-exciting generators ordinarily depend upon their residual magnetism at starting for building up their field excitation. In order that the machine may build up its magnetism wit-h certainty and quickly, it is desirable that the resistance of the fieldcircuit at starting should be as low as possible. Thus if the machine is designed to operate normally with an appreciable amount of resist; ance in the field-circuit this resistance can be out of circuit at starting in order to help the machine to build up its magnetism. In the self-exciting alternator described in my for mer patent above mentioned the field-circuit was provided with resistances in series with the source of shunt excitation in normal operation, and across the terminals of this resistance were connected the secondaries of the series transformers for furnishing the compounding. At starting no current flows through the series transformers, so that the resistances serve no useful purpose, but retard the building up of the field magnetization from the shunt excitationv It is therefore desirable to out these resistances out of circuit at starting. If, however, these resistances should be cut out not only at start ing, but also after the machine has built up its magnetism, the voltage of the machine would rise to an excessive amount. By my invention I so arrange the controlling means that while the resistance, may be readily cut out at starting it cannot be left out of circuit through carelessness ofan attendant.

My invention consists in the combination, with a self-exciting generator, of a resistance which is connected in the field-circuit of the generator during normal operation, means for cutting said resistance out of circuit at starting, and means for automaticallymoving the cutting-out means when released to cut said resistance into the fieldcircuit again.

My invention further comprises arranging the usual field-rheostat itself so that it may be used for cutting out the resistance at starting; and to this end my invention further consists in the combination, with a selfexciting generator, of a iield-rheostat comprising a resistance and a movable member coacting therewith to regulate the generator voltage and means for automatically returning said member a predetermined'distance when moved to its extreme high-voltage position and released.

'My invention in another aspect consists in the combination, with the self-exciting alternator of my former patent arranged with resistances in the field-circuit connected to the source of series excitation, of means for cutting said resistances out of circuit at starting and means for automatically cutting the resistance into circuit again when the controlling means is released by the operator.

My invention further comprises a novel connection of the rheostat, series transformers, and resistances whereby the number of transformer leads is reduced to a minimum.

My invention will best be understood by reference to the accompanying drawings, in which Figure 1 shows diagrammatically a selfexciting alternator of the type described in my former patent provided with a field-rheostat arranged in accordance with my invention, and Fig. 2 shows a detail view of a portion of the rheostat.

In the drawings, A represents the armature-winding of an alternating-current gen erator. For the sake of simplicity-this wind ing is shown as a Gramme ring. F represents the field-winding, the terminals of which are connected to the segments 0 c of a rectifying-commutator C. The commutator is provided with the polyphase arrangement of brushes 1) 6 described in my former patent. The arrangement and operation of a machine of the type illustrated is fully described in my former patent, and as far as the present invention is concerned it is sufficient that it be understood that a polyphase excitation from any suitable source is impressedvupon I I the brushes Z) l) and is rectified by the commutator C and delivered as direct current to the field-winding. I11 the drawings an arrangement of brushes suitable for threephase excitation is shown, the brushes being displaced from each other one hundred and twenty degrees and the cormnutator-segments 0 being each of substantially one hundred and twenty electrical degrees in length, so as to, engage one brush at the instant of leaving another brush. In the arrangement of Fig. 1 I have shown the polyphase excitation derived from the armature through the combination of an auxiliary winding on the armature and series transformers in the armature-circuit. The auxiliary winding is represented by a and furnishes the shunt excitation for the field. Resistances 1 7' are placed in series with the several phases of the auxiliary winding, and across the terminals of these resistances are connected the secondaries of transformers T T, the primaries of which are in series with the main armaturewinding. These transformers act to impress across the terminals of the resistance r in series with the auxiliary winding a compounding voltage. The series transformers are so connected with refer ance to the several phases of the auxiliary winding that the compounding voltage is displaced in phase ninety degrees from the voltage, due to the auxiliary winding, when the armatLire-current is in phase with the induced voltage-that is, when the load is non-inductive. This arrangement provides compounding for both inductive and non-inductive loads, as is fully described in my former patent, N 0. 789,476, above mentioned. Between the auxiliary winding a and the resistances r are inserted the variable resistances R of the field-rheostat by means of which the voltage of the machine is adjusted.

D represents a pivoted three-arm member, each arm carrying a contact (1, adapted to short-circuit a resistance R step by step by connecting the successive contact-points of the resistance to the contact-segment (Z, to which one of the coils a is connected. The arm D is shown. in Fig. 1 in. the extreme lowvoltage position, with all of the variable resistance in circuit. The circuit of each phase of the auxiliary winding may be traced from a terminal of coil a, to segmental contact (Z, movable contact (Z, resistance R, resistance r, to thcneutral conductor a. It is across the resistance 1' that the series transformers T are connected, and by placing the resistances 1- at the neutral point of the lieldcircuit only three leads from the transformers are required instead of six, as would be the care if the resistances 7'' were not placed at the neutral point. series transformers are at some distance from the rheostat, as may often be the case. As i This is of some importance if the seams clockwise direction, the resistances it are cut out step by step until the limit of the normal range of movement is reached, as shown on an enlarged scale in Fig. 2, when all of resistance R is short-circuited. At this point the arm strikes against a yielding stop comprising a pivoted arm E, normally held against a stop a by a tension-spring F. Beyond this stop is placed a contact-point connected to short-circuit all or nearly all of resistance 1-, which in. normal operation is retained in the field-circuit. At starting, arm D may be moved to engage this short-circuiting contact-point, and thereby to cut resistance 7' out of circuit. As has been heretofore explained, this resistance serves no useful purpose at starting when no current is flowing through the series transformers, but acts only as so much dead resistance, retarding the machine in building up its excitation. By cutting this out at starting, the machine is enabled to pick up much more quickly. If resistance 7' were left short-circuited, the generator voltage might rise to a dangerous value. To prevent this is the purpose of the yielding stop E, which presses upon arm I) and restores it, when released by the operator, to the position shown in Fig. 2, thereby automatically cutting resistance r into circuit again.

I do not desire to limit myself to the particular construction and arrangement of parts here shown, but aim in the appended claims to cover all modifications which are within the scope of my invention.

hat I claim as new, and desire to secure by Letters Patent of the United States, is

1. In combination with a self-exciting generator, a resistance connected in the field-circuit of said generator in normal operation, means for cutting said resistance out of circuit at starting, and. means for automatically moving the cutting-out means when released to out said resistance into the field-circuit again.

2. In combination with a self-exciting generator, a resistance connected in the field-ch"- cuit of said generator in normal operation, a movable member adapted to short-circuit said resistance at starting, and a yielding stop arranged to be engaged by said member and adapted to move it when released to break the short circuit.

3. In combination with a self-exciting generator, a field-rheostat comprising a resistance connected inv the field-circuit of said generator and provided with contact-1mints, a member adapted to move over said contact-points to vary the voltage of said. generator, a resistance in circuit with the field of said generator in normal operation, a short- 6 5 the arm D in Fig. 1 is moved in a counterl oircuiting contact for said latter resistance beyond. the normal range of movement of said member, and means for automatically returning said member to its normal range Ill when moved to engage said short-circuiting contact and released. a

4. In combination with a self-exciting generator, a field-rheostat comprising a resistance connected in the field-circuit of said generator and provided with contact-points, a member adapted to move over said contactpoints to vary the voltage of said. 'enerator, a resistance in circuit With the fie d of said generator in normal operation, a short-circuiting contact for said latter resistance beyond the normal range of movement of said member, and a yielding stop arranged to be engaged by said member when moved to engage said short-circuiting contact.

5. In combination with a self-exciting generator, afield-rheostat comprising a resistance and a movable member coacting therewith to vary the generator voltage, and a yielding stop arranged to be engaged by said member in its extreme high-voltage position.

6. In combination with a selfexciting generator, a field-rheostat comprising a resistance and a movable member coacting therewith to vary the generator voltage, and means for automatically returning said member a predetermined distance when moved to extreme high-voltage position and released.

7. In combination with an alternatingcurrent generator, a polyphase source of ex citation therefor derived from the generatorarmature, a field-rheostat comprising resistances incircuit with the several phases of said source and a movable member adapted to short-circuit said resistances simultaneously step by step to vary the generator voltage, and means for automatically returning said member a predetermined distance when moved to extreme high-voltage position.

8. In combination with an alternating-v current generator, a polyphase source of excitation therefor derived from the generatorarmature, a field-rheostat comprising resistances in circuit with the several phases of said source and a movable member adapted to short-circuit said resistances simultaneously step by step to vary the generator voltage, and a yielding stop arranged to be engaged by said member in its extreme high-voltage position. v

9. In combination with an alternating current generator, a polyphase source of excitation therefor derived from the generator armature, a field-rheostat comprising resistances in circuit with the several phases of said source and provided with contact-points, a member adapted to move over said contact-points to out said resistances simultaneously out of circuit step by step to vary the voltage of said generator, resistances in circuit with the several phases of said source in normal operation, short-circuiting contacts for said latter resistances beyond the normal range of movement of said member, and

means for automatically returning said member to its normal range when moved to engage said short-circuiting contacts and released.

10. In combination with an alternatingcurrent generator having a fieldwinding provided with a commutator, a source of alternating-current connected to said commutator, a resistance in series with said source, a transformer having its primary connected in series with the generator-armature and its secondary in shunt to said resistance, means for cutting said resistance out of circuit at starting, and means for automatically moving the cutting-out means when released to' out said resistance into circuit again.

11. In combination with a polyphase generator having a fieldwindingprovided with a commutator, a source of polyphase current connected to said commutator, resistances in series with the several phases of said source, transformers having their primaries connected in series with the several phases of the generator-armature and their secondaries in shunt to said resistances, means for cutting said resistances out of circuit at starting, and means for automatically moving the cuttingout means when released to out said resistance into circuit again.

12. In combination with an alternatingcurrent generator having a field-winding provided with a commutator, a source of alternating current connected to said commutator, a resistance in series with said source, a transformer having its primary connected in series with the generator-armature and its secondary in shunt to said resistance, a fieldrheostat, a short-circuiting contact for said resistance adapted to be engaged by the movable member of said rheostat when said member is moved beyond its normal range, and means for automatically returning said movable member when moved to engage said contact and released.

13. In combination with an alternatingcurrent generator having a field-winding provided with a commutator and brushes, a three-phase source of current derived from the generator-armature comprising three windings each having one terminal connected to a commutator-brush, three resistances each having one terminal in electrical connection with the other terminal of one of said windings and its other terminal connected directly to a common neutral point, and three transformers having their primaries in series With the armature and having one terminal of their secondaries connected together and their other terminals connected to the outer terminals of said resistances.

14:. In combination with an alternatingcurrent generator having a field-winding provided with a commutator and brushes, a three-phase source of current derived from the generator-armature comprising three windings each having one terminal connected. to a commutator-brush, three resistances each having one terminal in electrical connection with the other terminal of one of said windings and its other terminal connected directly to a common neutral point, three transformers having their primaries in series with the armature and having one terminal of their secondaries connected together and their other terminals connected to the outer terminals of said resistances, and means for cutting said resistances out of circuit at startmg.

15. In combination. with an alternating current generator having a field-winding provided with a commutator and brushes, a three-phase source of current derived from the generatorarmature comprising three windings each having one terminal connected to a commutator-brush, three resistances each having one terminal in electrical connection with the other terminal of one of said windings and its other terminal connected directly to a common neutral point, three transformers having their primaries in series with the armature andv having one terminal of their secondaries connected together and their other terminals connected to the outer terminals of said resistances, means for cutting said resistances out of circuit at starting, and means for automatically moving said cutting-out means when released to out said resistanccs into circuit again.

16. In combination with an alternatingcurrentgenerator having a field-winding provided with a commutator and brushes, a

! three-phase source of current derived from the armature comprising three windings each having one terminal connected to a commutator-brush, a field-rheostat comprising three variable resistances connected to the other terminals of said windings, three transformers having their primaries in series with the armature and each having one terminal of its secondary connected to a common neutral 5 point and its other terminal connected to one of the variable resistances, and resistances connected in shunt to said transformer secondaries.

17. In combination with an alternatingcurrent generator having a field-winding provided with. a commutator and. brushes, a three-phase source of current derived from the armature comprising three windings each having one terminal connected to a commutater-brush, a field-rheostat comprising three variable resistances connected to the other terminals o'f'said windings, three transformers having their primaries in series with the armature and each having one terminal of its secondary connected to a common neutral and its other terminal connected to one of the variable resistances, resistances connected in shunt to said transformer secondaries, and means for short-circuiting the last-11am ed 6 5 resistances at starting.

In witness whereof I have hereunto my hand this 13th day of July, 1905.

ERNST I W. AhllXANlllillSON. l \Vitnesses:

BENJAMIN B. HULL, I'IELEN Onronn. 

